HVAC and Electrical Terms


A device installed in the suction line of a HVAC system to prevent liquids (usually refrigerants) from entering the compressor.

AFUE (annual fuel utilization efficiency) is the ratio of yearly heat output of a furnace or boiler compared to the total yearly fossil fuel energy consumed by a furnace or boiler. The higher the rating, the more efficient it is.

Air Balancing
A process for HVAC system performance measurement, a term for distributing air through a system to precisely match the required amount.

Air Cleaners
Equipment that removes and controls the accumulation of various airborne pollutants and gases from the inside air to improve indoor air quality.

Air Conditioner
A piece of equipment that is used to control temperature and humidity of the inside air.

Air Diffuser
Also known as a supply air outlet which diffuses conditioned air into a space, providing uniform air flow throughout the space.

Air Duct
A pathway for distributing air from a HVAC system.

Air Exchange Rate
The rate at which outdoor air replaces indoor air, indoor pollutant levels can increase, expressed in one of two ways: the amount of changes of outside air per unit of time – air changes per hour (ACH); or the rate at which a volume of outside air enters per unit of time – cubic feet per minute (CFM). This rate is controlled through natural and/or mechanical ventilation.

Air Filter
A device for preventing dust, dirt, natural debris etc., from entering the HVAC equipment.

Air Handler
Air Handling Units (AHU) are typically cabinets containing a blower and accessories to distribute conditioned air through a duct system.

Air Infiltration
The unwanted entry of air into a building, due to a crack, leakage, temperature difference, or wind.

Air Vent
Typically installed on a boiler system, this device is used to remove unwanted air from a piping system.

A natural or artificial substance capable of causing an allergic reaction because of an individual’s sensitivity to that substance.

Ambient Air
The air external to a building or device.

Attic Fan
A powered fan, permanently installed, used to expel warm attic air to the outside and creating cross ventilation.

Attic Vent
A device used to allow for free air flow in an attic space, mainly to release heat and prevent condensation.


A powered fan used to distribute conditioned air or exhaust fumes in an HVAC system.

A piece of equipment used to heat water serving a central radiant heating system.

Boiler Pressure
The pressure in a boiler as measured, generally expressed in pounds per square inch gauge (psig).

British Thermal Unit (BTU)
The amount of heat necessary to increase the temperature of one pound of water one degree Fahrenheit.

Building Related Illness (BRI)
Occurs when the symptoms of a diagnosable illness are identified and can be attributed directly to building contaminants, usually airborne elements in a confined space.


A device that stores electrical charges for a motor in an HVAC system.

Carbon Dioxide (CO2)
A colorless, odorless gas with the abbreviation CO2 that is present in the atmosphere.

Carbon Monoxide (CO)
A colorless, odorless gas created during combustion that can be toxic in high concentrations.

Central Air Conditioning
A permanently installed air conditioning device that distributes conditioned air throughout an entire home/space.

Central Heating System
A permanently installed heating device that distributes heat throughout an entire home/space.

The process of burning a fossil fuel. The oxidation of a material by applying heat, which ignites oxygen with a material or fuel.

Combustion Chamber
Any complete or partially enclosed space in which combustion (burning of fuel) takes place.

Combustion Gases
The byproducts created during the combustion of a fossil fuel.

A device typically powered by electricity, used to compress refrigerant gasses in an air conditioning system.

The device in an HVAC system in which the refrigerant condenses from a gas to a liquid after it is superheated by compression.

Cooling Capacity
The amount of heat that an air conditioner is able to remove from a given space in one hour.


A device used in a duct system which varies the amount of air flow through a duct.

A machine for minimizing the level of humidity in a space.

Di-electric Union
A fitting, made of dissimilar metals, used in water piping systems to prevent electrolysis and reduce corrosion.

Diffusers and Grilles
Components of the ventilation system that supply and return air to and from a conditioned space and terminate a duct.

Dip Tube
An internal pipe inside the water heater that ensures the cold water enters the bottom of the water heater.

Duct Fan
A powered fan used to increase air flow in a particular duct.

Fabricated materials that distributes air throughout a conditioned space, typically made of galvanized metal or plastic.


Exhaust Ventilation
An HVAC term for the mechanical removal of air from a space.


The piping attached to a fossil fuel burning device that exhausts the combustion gases.

Forced Air System or Furnace
A heating system in which heated air is forced by a fan through ducts into the conditioned space.


Geothermal Heat Pump
A ground-source heat pump uses the earth to help heat or cool a refrigerant system.


Heat Loss
The heat energy that is lost from a building through the walls, roof and windows during winter.

Heating Load
The amount of heat necessary to maintain a specific indoor temperature; measured in BTUH per hour.

High efficiency particulate arrestor. This refers to an air filter that is made for applications where microscopic airborne particles or pollutants may cause health issues.

An appliance for increasing the relative humidity in a conditioned space.

HVAC is an acronym for heating, ventilation and air-conditioning.


Indoor air quality.


LED stands for light-emitting diode. It is type of solid-state lighting that uses a semiconductor to convert electricity into light. LED bulbs can be 6 – 7 times more energy efficient than conventional incandescent lights and cut energy use by more than 80 percent. The typical life span is 4 – 5 times longer than an incandescent bulb.


MERV Rating
An acronym for Minimum Efficiency Reporting Value. This is an industry-standard method of rating the effectiveness of air. A MERV rating goes from 1 to 16, 16 being the highest-rated efficiency.


Preventative Maintenance
Regular cleaning and inspection of HVAC equipment.

Programmable Thermostat
A type of thermostat that allows the user to program a schedule of times and temperatures to best suit their needs.


A measurement of thermal resistance used in the construction industry.

Radiant Floor
A method of heating using water or electricity to transfer heat to the conditioned space.

A device used to transfer heat to a conditioned space. Typically made of metal and used with boiler systems.

The chemical used in air conditioners and heat pumps, to transfer heat into or out of an interior space.


Seasonal Energy Efficiency Ratio (SEER)
A rating system used to calculate power and Btu’s. The higher the SEER rating, the lower the cost of operation.

Steam Boiler
A piece of equipment used to steam water and serve a central heating system.

Sump Pump
A pump used to remove water that has been collected to reduce the water burden around a building foundation.


A safety device used in gas burning equipment.


A specific area in a conditioned space.

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